USPS Plugin

So, I have downloaded and installed the USPS plug in found in these forums. I have the most recent one I found. I obtained API credentials and ID from USPS. The test function did not work, however it appears evident that most people do not get it to work. I had them convert my account to production server. The plug in page on the back end asks for the user ID and post code. Should the shipping module then work? Should my USPS shipping cost fro shop to customer address now be working? Because nothing has changed at all. What am I missing?